1. Field of the Invention
The invention pertains to compass data converters particularly with respect to converting 180X and 90X compass synchro data into 1/6 degree resolution digital step data. The invention may be utilized in commercial marine radar displays requiring compass heading data to be utilized to provide a north of course stabilized display mode.
2. Description of the Prior Art
Present day gyro compasses provide a wide variety of heading data output formats. Gyro compasses traditionally provide output data in 360X synchro, 180X synchro, 90X synchro and 1/6 degree step formats. The synchro formats are utilized to enhance accuracy and resolution. For example, in a 360X system a synchro is geared to the compass output shaft to effect one mechanical revolution for each compass spacial degree. In such a configuration the gear ratio is 360:1. In the 180X synchro system, the synchro is geared to effect one mechanical revolution for two compass spacial degrees. In a similar manner the 90X synchro is geared to effect one mechanical revolution for four spacial degrees. The 1/6 degree step data output is generally utilized in a 360X system and provides a standard 3 digit grey code representing the 1/6 degree steps.
In gyro compass systems it is generally desirable to convert the output data thereof to digital format for transmission to remote apparatus. It is also desirable, for acceptable performance, to provide a minimum of 1/6 degree resolution. Therefore, it is a desideratum of the prior art to provide economical, low power apparatus to convert the wide variety of heading data formats available to digital step data with a minimum of 1/6 degree resolution. A low cost, low power prior art converter for transforming 360X synchro data to 3-digit grey code with 1/6 degree resolution is found in U.S. Pat. No. 4,031,531 issued June 21, 1977, entitled "Synchro-to-Digital Converter". Said patent 4,031,531 is incorporated herein by reference in its entirety. Further 360X converters may be found in U.S. Pat. No. 4,398,353 issued Aug. 16, 1983, entitled "Compass Data Converter" and in U.S. Pat. No. 4,401,932 issued Aug. 30, 1983, entitled "Syncro-to-Step Data Converter". Patents 4,398,353 and 4,401,932 are incorporated herein by reference in their entirety.
Apparatus is known in the prior art for providing 1/6 degree step data from 180X or 90X synchro-type compass systems but such apparatus is electromechanical and hence bulky, unreliable, and expensive. One such prior art system utilizes the synchro-type compass data to position a synchro servo system having an output linked through a gear train to a 1/6 degree step motor to provide the 1/6 degree compass step data. Another prior art system utilizes the synchro-type compass data to position a synchro servo system having an output linked through a gear train to an optical disc and decoder to provide the 1/6 degree compass step information. Because of the requirements of the synchro servo systems and the gear trains, each type of compass data output format requires a unique assembly. Additionally, the apparatus requires an excessive amount of space because of the synchro servo systems and the gear trains.
Synchro-to-digital converters for the various synchro data output formats are known which interface to the desired compass synchro data formats. Such converters, however, tend to be excessively expensive. The use of such converters in a low cost commercial compass system or commercial radar system would tend to be prohibitive.